1. Field of the Invention
The present invention relates to non-contact masks used with electromagnetic energy sources for projection of patterns for etching and ablation and more particularly to a reflective mask with an extended lifetime.
2. Description of the Background Art
U.S. Pat. No. 4,923,772 issued May 8, 1990 to Kirch et al. entitled, "HIGH ENERGY LASER MASK AND METHOD OF MAKING SAME" describes a mask and methods for making masks for use with a laser projection etching system. The unique mask is able to withstand the fluences of the high energy and high power lasers used without degrading. Specifically, the new projection etching masks are fabricated of patterned multiple dielectric layers having alternating high and low indices of refraction on a UV grade synthetic fused silica substrate in order to achieve maximum reflectivity of the laser energy in the opaque areas and maximum transmissivity of the laser energy in the transparent areas of the mask.
U.S. Pat. No. 4,317,876 issued Mar. 2, 1982 to Haering entitled, "METHOD FOR PRODUCING HIGH RESOLUTION RECORDING MEDIUM" discloses a method for producing a high resolution, multi-color recording medium comprising the steps of applying a photosensitive masking layer to a substrate, exposing the masking layer, and then developing the masking layer to expose a patterned portion of the underlying substrate. A reflecting layer is then applied over the remaining masking layer and exposed substrate, and then the remaining masking layer is removed, leaving only that portion of the reflecting layer directly over the substrate. A uniformly thick interference layer is then applied over the substrate and the remaining portion of the reflecting layer, and a second reflecting layer is then applied using the same procedures described above in connection with the first reflecting layer.
U.S. Pat. No. 4,842,617 issued Jun. 27, 1989 to Wojnarowski et al. entitled, "EXCIMER LASER PATTERNING OF A NOVEL RESIST USING MASKED AND MASKLESS PROCESS STEPS" describes a dual layer resist configuration for photo-patterning high resolution conductive patterns on underlying polymeric or ceramic substrates, particularly substrates exhibiting surface roughness and non-planar design features such as channels, bosses and ridges. More particularly, a thin underlayer of ablatable photoabsorptive polymer is disposed on a metal coated substrate, after which a thicker layer of substantially transparent material is disposed over the polymer. A beam of laser energy, such as that produced by an ultraviolet excimer laser, is directed through the upper layer and is absorbed by the lower layer which is ablated and simultaneously removes the thick layer above it. This results in the ability to etch high resolution features on polymeric and other substrates, particularly copper coated polyetherimide circuit boards. An alternate method is disclosed which employs two laser exposure steps with the first step being a masked operation on only an ablatable layer and with the second step being an unmasked operation on a dual layer material.
U.S. Pat. No. 4,877,480 issued Oct. 31, 1989 to Das entitled, "LITHOGRAPHIC TECHNIQUE USING LASER FOR FABRICATION OF ELECTRONIC COMPONENTS AND THE LIKE" discloses a microlithographic process of fabricating electronic components, such as, for example, integrated circuit chips and thin film read/write heads for computer disk systems, in which a laser is used to each features defined by a mask. The laser is selected whose radiation will be absorbed by the workpiece being etched, and the masking material is selected so as to be highly reflective of the laser radiation. The masking material is patterned in a conventional manner so as to expose the portions of the workpiece material to be etched. When the laser is directed to the workpiece, the laser radiation etches the portions of the workpiece not protected by the mask. The depth of the recess formed by the laser can be limited by depositing an etch stop layer of reflective material. The depth of the recess formed by the laser can be limited by depositing an etch stop layer of reflective material on a substrate, followed by an intermediate layer of workpiece material to be etched, and then the reflective mask. The laser radiation etches the intermediate layer through the mask to the etch stop layer, which prevents radiation from etching the workpiece further.